Patient data from a new study showed that around 20 percent of people living with dementia also experienced at least one type of vision impairment. Scientists probe the link between the two.
It’s long been said that the eyes are the windows to the soul, but more and more research supports findings that the eyes are also windows to providing a better understanding of what causes dementia and how to prevent it.
One such study from the Journal of the American Medical Association Ophthalmology demonstrates just how prevalent vision impairment is among patients with dementia. The study of 2,767 adults over the age of 65 in the U.S. found that nearly 20 percent with dementia also experienced at least one type of vision impairment — contrast sensitivity impairment, near visual acuity, and distance acuity impairment.
Contrast sensitivity impairment — the inability to tell the difference between two similar colors or shades of gray — made up 15 percent of the visual impairments observed among patients in the study. According to WebMD, impairment is often caused by conditions such as glaucoma, cataracts, macular degeneration, myopia, or optic neuritis.
Impairment of near visual acuity — the ability to see objects at close range — constituted 9.7 percent of observed instances of vision impairment among the patients with dementia, while, conversely, distance acuity impairment, or the inability to see objects at a distance, amounted to 4.9 percent.
Visual impairments are thought to contribute to dementia because the eye-brain connection that begins at the retina relies on an intricate neurological network to support cognitive function. A breakdown in this network results in cognitive impairment and eventual decline.
Additionally, symptoms of visual impairments can signal potential instances of dementia, as with the case of posterior cortical atrophy – a rare type of dementia whose onset symptoms include blurred vision and hallucinations.
The Lancet Commission on Dementia prevention, intervention, and care, a global project that gets scientists to review the evidence for risk factors of dementia every few years, included two new risk factors in its recent update to its 2020 report on dementia risk factors: vision loss and high cholesterol.
Untreated vision loss is cited as a risk factor for dementia, specifically “cortical blindness” — which is vision loss that isn’t caused by problems with the eyes.
Researchers have been developing eye tests, such as retina scans that use imaging technology to support both overall vision health and help detect early signs of dementia, including the build-up of beta-amyloid plaques that constrict blood flow to the brain, up to 20 years before the disease develops.
“The retina is the only central nervous system organ not shielded [by] bone that can be imaged directly and repeatedly,” neuroimmunology and neuro-ophthalmology expert Maya Koronyo-Hamaoui told Being Patient.
Koronyo-Hamaoui noted, however, that the timeline on when some of the scans will become more widely available is hard to predict.
Lisa Power is a recent graduate of the Columbia University Graduate School of Journalism.